The present invention relates to the polymerization of olefins in the presence of catalysts known in the art as ziegler catalysts.
Ziegler catalysts are commonly formed by reducing a transition metal compound with an organometallic compound. The reduced transition metal compound is then used, in conjunction with an activator, which may be the same or a different organometallic compound, to polymerize olefins, especially ethylene, in the presence of an inert solvent. A molecular weight regulator, such as hydrogen, may be used with these catalyst systems, as taught by Vandenberg in U.S. Pat. No. 3,051,690.
Ziegler et al, in U.S. Pat. No. 3,070,549 teach that catalysts can be prepared by reduction of transition metal salts with organometallic compounds of magnesium or zinc, either alone or in combination with organoaluminum compounds. Yields in the order of 500 grams of polyethylene per gram of transition metal were obtained.
Ziegler et al, in U.S. Pat. No. 3,392,162 teach that the organometallic compound used as reducing agent for the transition metal salts can be mixed complexes of organolithium and organoaluminum, organomagnesium or organozinc compounds. Similar low yields of polyethylene were obtained.
Fletcher et al, in U.S. Pat. No. 3,801,558, teach that organomagnesium compounds containing a controlled amount of an ether or amine complexing agent for the magnesium compound, when used to reduce the transition metal salts gives higher catalytic activity. Catalyst efficiencies as high as 180,000 grams of polyethylene per gram of transition metal were obtained at a pressure of over 100 psig.